1. Field of the Invention
The present invention relates to a method for setting a power control initial value by using an indication light in visible light communications and a transmission/reception (Tx/Rx) apparatus using the method. More particularly, the present invention relates to a method for setting a power control initial value of a visible light communication transmitter by using an indication light radiated from the visible light communication transmitter in order to align a position between the visible light communication transmitter and a visible light communication receivers and a transmission/receive apparatus using the method in a visible light communication system.
2. Description of the Related Art
Recently, as luminous efficiency of Light Emitting Diodes (LEDs) has been improved in, the LEDs are more commonly used not only in a special illumination market, such as handheld devices, displays, automobiles, traffic lights, advertising boards, etc., but also in the general illumination market, such as fluorescent lamps, incandescent electric lamps, etc. Especially, the luminous efficiency of LEDs has already surpassed that of incandescent electric lamps, and products superior to incandescent electric lamps are appearing in the marketplace. Also, as interest in optical wireless technology complementary to RF technology has lately increased because of an exhaustion of the frequencies in a Radio Frequency (RF) band, the possibility of false cross among wireless communications, an increase of the security requirement for communications, the advent of a very high-speed ubiquitous communication environment of fourth generation mobile communication (4G) wireless technology, etc., studies are being carried out on visible light wireless communications using visible light LEDs in many enterprises and research institutes, etc.
Communications for transmitting information by using visible light have merit such as a wide use band and the ability to be freely used without being subject to regulation. Also, the visible light communications have merit in that the reception range of information can be accurately sensed because a spot where light reaches or a direction in which the light moves can be seen. Accordingly, the visible light communications have reliability in an aspect of security, and also have merit such as the ability to be driven with low electric power in the aspect of power consumption.
As an example where visibility characteristics of visible light is applied, a scheme of aligning a transceiver by using an indication light can be cited. This scheme corresponds to a scheme where if the visible light communication transmitter radiates an indication light made up of a visible ray that can be seen before performing communications, a user visually checks the indication light, and controls the visible light communication transmitter or the visible light communication receiver so that light can accurately reach a light receiving unit of the visible light receiver. Since the application of the above scheme can cause a light divergence angle of the visible light communication transmitter to be acute, an advantage can be obtained in the aspect of power efficiency and security.
Subsequently, a description will be made of a configuration and an operation of a visible light communication apparatus using the scheme of aligning a transceiver by using indication light.
FIG. 1 is a block configuration diagram illustrating an example of a general visible light communication transceiver using an indication light. With reference to FIG. 1, a visible light communication transmitter 101 (hereinafter, referred to as “transmitter 101”) includes an encoder 105, a modulator 107, a Direct Current (DC) supply 111, a controller 103, and a switch 109. Herein, the encoder 105 receives data to be transmitted, and performs channel coding on the received data. The modulator 107 modulates channel-coded information. The DC supply 111 generates an indication light necessary to align a position between the transmitter and a receiver at the very beginning of communication. The controller 103 controls operations of respective configuration elements of the transmitter 101. The switch 109 distinguishes between a period during which the indication light is generated and another period during which data is transmitted, and connects the modulator 107 or the DC supply 111 with a luminous clement under the control of the controller 103.
A visible light communication receiver 102 (hereinafter, referred to as a “receiver 102”) includes a demodulator 108, a decoder 106, a received signal strength meter 110, and a controller 104. Herein, the demodulator 108 demodulates a received signal. The decoder 106 receives a demodulated signal, and performs channel decoding on the demodulated signal. The received signal strength meter 110 measures the strength of the received signal. The controller 104 controls operations of respective configuration elements of the receiver 102 during reception of data.
FIG. 2 is a flowchart illustrating a power control operation during transmission/reception of data in a general visible communications using an indication light. Referring to FIG. 2, the visible light communication apparatus begins to operate, and in step 210, the transmitter 101 enables the DC supply 111 to generate an indication light in order to align a position between the transmitter 101 and the receiver 102. In step 220, the indication light radiated from the DC supply 111 included in the transmitter 101 is checked by a user, and then a communication position between the transmitter 101 and the receiver 102 is aligned. If the position alignment between the transmitter 101 and the receiver 102 has been completed, the procedure moves to step 230, and the transmitter 101 begins to transmit data to the receiver 102. In step 240, the receiver 102 receives the data from the transmitter 101. In step 250, the receiver 102 measures the strength of the received signal by using the received signal strength meter 110. If the strength of the received signal is stronger than or weaker than a prescribed threshold range according to a result of the measurement, the procedure proceeds to step 260 to request the transmitter 101 to adjust the strength of an output signal thereof. In step 250, if the strength of the received signal is in the range of the prescribed threshold range, the strength of a current output signal is maintained. Thereafter, in step 270, it is determined whether Tx/Rx operations are completed. If it is determined in step 270 that the Tx/Rx operations are completed, the procedure goes to step 280 to complete the Tx/Rx operations. If it is determined in step 270 that the Tx/Rx operations are not completed, the procedure goes back to step 230 to repeat the performance of the Tx/Rx operations until the Tx/Rx operations are completed.
As described in the Tx/Rx operations of the visible light communication apparatus, in a case where the strength of a transmitted signal changes as variations occur in a distance between the transmitter and the receiver and in an environment thereof, the power control adjusts the strength in electric power of the transmitted signal from the transmitter according to feedback information of the receiver power control, and causes a signal received by the receiver to be maintained.
To examine, in the aspect of power control, the prior scheme where the position alignment is implemented by using the indication light, the transceiver initiates the power control after the transmitter has begun to transmit the signal following the completion of the position alignment using the indication light. Accordingly, so that the transmitter may reach an adequate output power level, the transmitter has to go through a process for regulating transmitted power several times. When the transmitter is in the process for regulating transmitted power, the receiver receives the signal having the strength stronger than or weaker than an adequate power level. In this case, problems occur in that electric power is excessively consumed until an adequate output power level is reached, or unstable reception of the signal is caused by the use of low electric power.